turbines 5

turbine design

• case

• stator vanes

• shroud ring

• rotor blades

turbine case

encloses turbine

attaches combustor and exhaust at each end

shroud ring

minimize gas loss over the turbine blades (blade tip clearance)

turbine purpose

Convert kinetic (velocity) and heat energy of combustion gasses into mechanical energy to drive fan, propeller, compressor, accessories

each turbine stage contains a row of _______

stationary vanes followed by rotating blades

types of turbines

axial flow

radial inflow

axial flow

airflow is front to back, parallel to centre shaft

radial inflow

combustion gasses are guided by stators into rotors and exit at center

APU

stator and rotor blades are _____ ducts

convergent

nozzle guide vane

first start of stators aft of combustion chamber

counter rotating spools

• Dampens gyroscopic effect and vibrations

• Improve aerodynamic airflow efficiencies

counter rotating spool N1

LP counterclockwise (aft looking forward)

counter rotating spool N2

HP clockwise (aft looking forward)

3 spool engine spool sizes

low stage (N1) shaft is smaller diameter than IP stage (N2) shaft which is smaller diameter than HP N3 stage

stator blades

form nozzles that direct air at correct angle to turn turbine rotor and increase velocity

rotor

consists of shaft, disk (hub or wheel) and blades

how are rotor blades attached

attached using fir tree root to contain radial motion

blades are locked axially using peening, welding, lock tabs or rivets

rotor blade shape

blades are open tip or shrouded to form an outer band

rotor blades are attached using _____ to contain _____ motion

fir tree root, radial

rotor blades are locked _____ using peening, rivets, welding, lock tabs

axially

open tip rotor blades

high speed (N2)

shrouded rotor blades

low speed (N2)

turbine RPM is caused by 

impulse or reaction forces

impulse forces

• Blades change direction of airflow with minimal change in pressure or velocity

• Turbine wheel absorbs the impact force and converts it into rotary motion

reaction forces

• Blades form a series of convergent ducts

• Exit velocity is pushed off the blade > blade rotates (action-reaction principle)

impulse-reaction forces

Maintains uniform velocity and pressure drop along entire blade length

impulse reaction blade tip

Blade tip is reaction shaped

impulse reaction blade base

Blade base is impulse shaped